1. Field of the Invention
The present invention relates to radiation detection and, more specifically, to the detection of beta emitting radionuclides in a flowing fluid medium.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Radionuclides in water and liquid food products are a serious public health threat that the Food and Drug Administration (FDA) in conjunction with the Environmental Protection Agency (EPA) seeks to control through stringent regulations. The EPA currently mandates specific limits for radionuclides in drinking water: radium 226/228 (5 pCi/L); alpha emitters (15 pCi/L) (not including radon and uranium); beta emitters (4 mrem/year); and uranium (30 μg/L). Radionuclide in other liquid foodstuffs, such as milk, are likewise regulated.
Radionuclides in milk are a concern primarily because of the quantity of milk consumed by children. Children have a higher cellular activity than adults and are more susceptible to the damaging effects of ionizing radiation. Strontium-90 (Sr-90) is of particular concern because of its chemical similarities to calcium. These similarities cause compounds of Sr-90, when ingested, to be deposited in biological systems, exposing them to radiation damage. Although the US Environmental improvement Agency has found that present levels of Sr-90 in milk attributable to atmospheric testing of nuclear weapons are barely detectable, concern still exists for possible contamination from other sources, including malicious attempts at food adulteration. For that reason, the food and Drug Administration has established a program of food surveillance. Having a means for efficiently monitoring of the milk supply for such radionuclides is, therefore, of vital importance.
Present detection techniques for monitoring for radionuclides in liquid foodstuff, such as milk, require collection and processing of grab samples. For example, a technician may perform periodic testing of a municipal water supply by drawing a representative water sample and sending it to a lab for off-line analysis. In the lab, the sample is tested by performing a solid-phase extraction technique to isolate specific radionuclides, or one of many other possible concentration and radiochemical analysis techniques. In the case of solid-phase extraction, the analyte is isolated by pulling a sample through a special resin coated filter membrane and subsequently assaying the membrane using a common counting technique.
Solid-phase extraction and other radiochemical techniques for isolating radionuclides require substantial time to complete. In the time it takes to sample and test an analyte, significant amounts of contaminated liquid may have already entered the food supply. Halting the movement of product while awaiting test results would prevent this, but would be impractical since such action would have a severe negative impact on manufacturing efficiency and productivity.
In addition to Sr-90, milk contains significant amounts of the naturally occurring radioactive isotope Potassium-40 (K-40). K-40 is relatively benign when consumed because it has a long half-life (1.250×109 years) and is maintained in equilibrium at very low concentrations in the body through homeostatic processes. Sr-90 is hazardous because it and its radioactive decay product, Yttrium (Y-90), deposit in critical organs such as the bones. Within the bones, their respective beta emissions irradiate large volumes of tissue. Further, both Sr-90 and Y-90 build up within the body (long biological half-life), displacing beneficial calcium.
K-40 decays to produce both a very strong beta (0.455 MeV) and gamma (1.46 MeV) emission. Sr-90 decay produces a single, strong beta (0.196 MeV) emission as well, along with its daughter radionuclide, Y-90 beta (0.935 MeV) emission. Consequently, it is exceedingly difficult to differentiate K-40 and Sr/Y-90 when only carrying out gross-beta count analysis. Since both radionuclides would potentially be present in milk, it is important that analysis techniques be able to differentiate between the two beta-emitters in order to quantify the presence of Sr-90. Current techniques for differentiating the two beta emitters merely further increase the time required for analysis of a sample.
Accordingly, a need exists for an online means for testing liquid foodstuff or water for radionuclides that allows for near real-time detection with minimal impact on processing of the product. Further, a need exists for an online means for testing liquid foodstuff that can differentiate between Sr-90 and K-40 without the need for off-line analysis. The present invention satisfies this need and others as described below.